One of major requirements for a next-generation wireless access system is high data rate. To this end, research is being conducted on various technologies such as Multiple Input Multiple Output (MIMO), Cooperative Multiple Point Transmission (CoMP), relay, etc.
A legacy wireless access system mainly considers only one carrier even when downlink and uplink bandwidths are configured differently. For example, a wireless communication system having one carrier configured for each of downlink and uplink and forming symmetry between downlink and uplink bandwidths was provided based on a single carrier.
However, considering that frequency resources are currently full, in order to ensure a wide bandwidth capable of satisfying higher data rate, each of scattered bandwidths is designed to satisfy basic requirements for operating an independent system and carrier aggregation (CA)/multiple cells technology is adopted to aggregate a plurality of bandwidths with a single system.
Here, a bandwidth-based carrier capable of independently operating may be referred to as a component carrier (CC). In order to support increased transmission capacity, the latest 3rd Generation Partnership Project (3GPP) Long Term Evolution-Advanced (LTE-A) or 802.16m system continuously extends its bandwidth up to 20 MHz or above. In this case, one or more CCs are aggregated to support wideband. For example, if one CC supports a bandwidth of 5 MHz, 10 MHz or 20 MHz, up to 5 CCs are aggregated to support a system bandwidth of up to 100 MHz.
However, to achieve maximum performance of the above technology, downlink control channels for a legacy system may not be used.